From Dog

Microfilaremia is defined as the presence of microfilaria in blood smears when observed under the microscope.

The absence of microfilaremia in confirmed cases of heartworm disease is defined as 'occult' due to immature worms (prepatent) or unisex infections[1].

The presence of microfilaria usually equates to infections with Dirofilaria immitis, but other parasites can cause microfilaremia, including:


  1. Rishniw M et al (2012) Sex ratios of Dirofilaria immitis in naturally infected dogs show female bias at low worm intensities. Res Vet Sci 93(3):1324-1328
  2. Wongkamchai S et al (2013) Rapid detection and identification of Brugia malayi, B. pahangi, and Dirofilaria immitis by high-resolution melting assay. Vector Borne Zoonotic Dis 13(1):31-36
  3. Otranto D et al (2013) Vector-borne helminths of dogs and humans in Europe. Parasit Vectors 6:16